Remark 2.4 We note that the idea of using the Galerkin methods to discretize the time
fractional calculus operators was firstly developed by McLean and Mustapha
[1]}, [2]}, [3]}, [4]}.
The L1 scheme [5]}, [6]} is widely used for the discretizations of
the fractional diffusion equations. Jin et al. [7]} discovered that the L1 scheme is equivalent to
discretization eq:Stau with uniform temporal grids. For the numerical
analysis of discretization eq:Stau with nonuniform temporal grids, we
refer the reader to [8]}, [9]}.

